Processes for cracking hydrocarbon oils generally comprise contacting and reacting hydrocarbon oils with a cracking catalyst in a cracking zone under cracking conditions, separating cracked products and the catalyst, circulating the catalyst to a regeneration zone and regenerating the catalyst therein, circulating at least a part of the regenerated catalyst back to the cracking zone. The object of regenerating the catalyst is to maintain the cracking activity of the catalyst.
Some hydrocarbon oils contain impurities, such as nickel, vanadium, iron and the like. If impurities contained in the hydrocarbon oil, such as nickel, vanadium, iron and the like, are deposited onto the catalyst containing a molecular sieve, the catalyst will thus be deactivated and the distribution of cracked products will be affected. In order to solve this problem, a reduction zone is added in some processes for cracking hydrocarbon oils.
U.S. Pat. No. 4,345,992 discloses a process for catalytically cracking of hydrocarbon oils. The process comprises contacting a hydrocarbon oil with a granular cracking catalyst in a cracking zone under cracking conditions, transferring continuously a part of said cracking catalyst to a regeneration zone where carbon deposits on the catalyst are removed by burning, then transferring continuously the regenerated catalyst to a reduction zone where said catalyst contacts with a reducing gas under such reduction conditions in which the harmful effect of impurity metals can be decreased, wherein a gas seal is used at the upstream of the reduction zone to ensure that the main portion of the unexpended reducing gas enters the cracking zone, and transferring continuously the reduced catalyst to the cracking zone. Said catalyst includes various conventional cracking catalysts, such as zeolite-containing cracking catalysts and amorphous aluminosilicate catalysts.
U.S. Pat. No. 4,623,443 discloses a process for hydrogenation of olefins. The process comprises cracking a hydrocarbon with a regenerated catalyst having a metal coat under cracking conditions in a cracking zone; transferring continuously said catalyst to a regeneration zone, contacting said catalyst with an oxygen-containing gas to regenerate said catalyst; transferring continuously a part of the regenerated catalyst to said cracking zone; meanwhile, transferring the other part of the regenerated catalyst to a reduction zone where said catalyst contacts with a reducing gas under conditions in which metals on the catalyst are reduced; transferring the cracked hydrocarbon to a separation zone where hydrogen and olefins are separated from the cracked products; contacting at least a part of said hydrogen and olefins with the reduced catalyst in a hydrogenation zone to hydrogenate the olefins; and finally transferring said catalyst to the regeneration zone.
U.S. Pat. No. 4,623,443 further discloses a process for continuous hydrogenation of olefins. The process comprises, under regeneration conditions, contacting a deactivated and metal-contaminated cracking catalyst with an oxygen-containing gas to obtain a regenerated and metal-contaminated catalyst; contacting the regenerated and metal-contaminated catalyst with a reducing gas under reduction conditions to obtain a reduced, regenerated and metal-contaminated catalyst and finally immediately contacting the reduced, regenerated and metal-contaminated cracking catalyst with a mixture of hydrogen and olefins to hydrogenate said olefins under hydrogenation conditions.
U.S. Pat. No. 4,623,443 also discloses a process for converting hydrocarbons. The process comprises (1) contacting a hydrocarbon which contains metals with an active catalyst in a reaction zone under cracking conditions to obtain cracked products and a catalyst that has been partially deactivated and metal-contaminated; (2) separating the cracked products and the partially deactivated and metal-contaminated catalyst; (3) fractionating said cracked products into hydrogen, olefins and other hydrocarbons; (4) contacting said partially deactivated and metal-contaminated cracking catalyst with an oxygen-containing gas under regeneration conditions to obtain a regenerated and metal-contaminated catalyst; (5) circulating a part of said regenerated and metal-contaminated catalyst to said reaction zone; (6) contacting the other part of the regenerated and metal-contaminated catalyst with a reducing gas under reduction conditions to obtain a reduced, regenerated and metal-contaminated catalyst; (7) contacting said reduced, regenerated and metal-contaminated catalyst with hydrogen and olefins under hydrogenation conditions to obtain hydrogenated olefins and a reduced, regenerated and metal-contaminated catalyst that is partially coked; (8) separating said hydrogenated olefins and said partially coked, reduced, regenerated and metal-contaminated catalyst; (9) circulating the hydrogenated olefins to the fraction system according to (3); (10) circulating the partially coked, reduced, regenerated and metal-contaminated catalyst to (4) to carry out regeneration.
In recent years, requirements of fuel standards worldwide become more and more stringent for the sake of environmental protection. For instance, in China, “Criteria for Controlling Hazardous Materials in Automobile Gasoline” was regulated by the National Quality Monitoring Bureau in 1999. Sulfur content in gasoline should be less than 800 ppm according to the requirement of the Criteria. More Stringent requirement of gasoline sulfur content i.e. less than 30 ppm, is regulated according to the Europe III Emission Standard of Fuel Oil. In fact, more than 90% of sulfur in gasoline are from FCC gasoline. In the other hand, more and more sour crude from the middle-east countries are processed in many Chinese refineries as FCC feedstock; meanwhile, crudes are getting more and more heavier in recent years. Therefore, there needs to develop a cracking catalyst with higher cracking activity and desulfurizing ability and a cracking process with higher ability for cracking and desulfurizing of heavy oil.
U.S. Pat. No. 6,036,847 and its European counterpart patent EP 0,798,362A2 disclose a process for fluidized catalytic cracking of hydrocarbons, wherein said hydrocarbon feedstock is cracked in a cracking zone without adding hydrogen, and all particles, including catalyst particles, are circulated continuously between a cracking zone and a regeneration zone. In said process, besides said particles, there are additional particles which have a lower activity for cracking hydrocarbon oils than the catalyst particles, said activity being based on the fresh catalyst particles. The particles consist essentially of titanium oxide and an inorganic oxide other than non-titanium oxides. Said inorganic oxide other than non-titanium oxides contains a Lewis acid supported on alumina, and the Lewis acid is one selected from the group consisting of the following elements and their compounds: nickel, copper, zinc, silver, cadmium, indium, tin, mercury, thallium, led, bismuth, boron, aluminum (non alumina) and germanium. The sulfur content of FCC gasoline as the cracked product is decreased because of the use of a titanium oxide-containing adjvuant.